Constrained acetabular trialing system

ABSTRACT

A trial head and shell for use in trial reduction of hip implants, and particularly bipolar implants, having locking features that prevent the head from dissociating from the shell during trialing, yet which allow the head and shell to be readily assembled and disassembled in the operating room. A cut-out region is formed in an outer bearing surface of the head. The cut-out region allows the head to pass through a trial shell opening and into the shell, yet is oriented such that when the head is associated with a femoral neck, the head cannot disassociate from the shell. Orientation indicators can be provided for use in assembly and disassembly. The trial head and associated shells can be provided in the form of a surgical kit including hip implants. Methods of use are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. provisional patent applicationNo. 60/863,462, filed Oct. 30, 2006, which is pending.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable

FIELD OF THE INVENTION

The present invention relates generally to trialing systems forconstrained hip implants, and more particularly to trialing systems forbi-polar hip implants.

BACKGROUND OF THE INVENTION

When implanting hip prostheses, trialing systems are used to verify thatthe surgeon is using the correct size of shell and head. The presentinvention provides an improved trialing system for use with constrainedhip implants, including particularly bi-polar hip implants. Examples ofbi-polar hip implants are found in U.S. Pat. No. 4,241,463 (Khovaylo)and U.S. Pat. No. 4,798,610 (Averill et al.), both of which areincorporated herein by reference.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the invention to provide a trialing system for use inimplanting a hip prosthesis in a patient.

It is another object of the invention to provide a trialing system thatis particularly adapted for use in trialing for a bipolar implant.

It is another object of the invention to provide a trialing systemhaving a locking feature that prevents a trial head from dissociatingfrom a trial shell during trial reduction, yet which readily assemblesand disassembles in the operating room.

It is yet another object of the invention to provide a trialing systemhaving a locking feature that prevents a trial head from dissociatingfrom a trial shell during trial reduction, yet which is easy tomanufacture, clean and sterilize.

These and other objects and advantages of the invention are achieved byproviding a trial head and an associated trial shell having thefollowing characteristics. An outer surface of the trial shell isconfigured for receipt within the acetabulum. The trial shell has asubstantially spherical bearing cavity formed therein for closelyreceiving the trial head during trial articulation, the bearing cavityextending beyond 180 degrees. The bearing cavity is accessible via atrial shell opening in the trial shell. The trial shell opening includesa head entry portion configured to allow the trial head to pass throughthe trial shell opening and into the bearing cavity. The head entryportion has a diameter that is less than a diameter of the bearingcavity.

The trial head has a bearing portion and a rim portion. The rim portionis configured to receive a femoral neck during trial articulation. Thebearing portion has a substantially spherical outer bearing surface, thebearing surface having a diameter greater than the diameter of the headentry portion of the trial shell opening. A cut-out region is formed inthe outer bearing surface. The cut-out region has a diameter that isless than the diameter of the head entry portion of the trial shellopening. The cut-out region is positioned such that when a femoral neckis disposed in the rim portion, the trial head is retained within thebearing cavity of the trial shell. When the cut-out region of the trialhead is aligned with the head entry portion of the trial shell opening,the trial head can pass through the trial shell opening and into thebearing cavity of the trial shell. The trial head is retained in thebearing cavity when the cut-out portion is not aligned with the headentry portion.

In a preferred embodiment, the cut-out region is cylindrical and extendsalong the bearing portion between opposing edges of the rim portion. Thecut-out region is preferably obliquely angled relative to the rim of thetrial head. The cut-out region is preferably angled at between about 60and about 70 degrees relative to the rim portion of the trial head, suchas at about 65 degrees.

The head entry portion of the trial shell is preferably cylindrical anddirectly adjacent the bearing cavity. The head entry portion is sized toclosely receive the cut-out region of the trial head. The cut-out regionis sized to closely pass through the head entry portion of the openingof the trial shell.

An orientation indicator is preferably provided on the trial head. Theorientation indicator is positioned to indicate alignment between thecut-out region of the trial head with the head entry portion of thetrial shell. In one preferred embodiment, the orientation indicator is aflat formed along the rim portion, the flat being substantially parallelto the cut-out region. An orientation groove can be formed along thecut-out region between the cut-out region and the orientation indicator.

Methods of using the instruments are provided. In one preferred method,a femoral neck is oriented in the femur of the patient for use in trialreduction. A trial head and associated trial shell having thecharacteristics described herein is provided, such as in the form of akit having multiple sizes of trial shells and heads. The surgeon alignsthe cut-out region of the trial head with the head entry portion of thetrial shell opening, inserts the trial head through the trial shellopening and into the shell bearing cavity, and rotates the trial headwithin the bearing cavity in order to bring the cut-out region out ofalignment with the head entry portion. The surgeon inserts the femoralneck into the neck bore of the trial head. The surgeon performs trialreduction on the patient's hip using the trial head and the trial shell.Once trialing is complete, the trial head is removed from trial neck,the cut-out region is rotated back into alignment with the head entryportion of the trial shell opening, and the trial head is removed fromthe trial shell.

The instruments are provided in the form a surgical kit. The kit mayinclude one or more bipolar hip implants. The kit includes at least onetrial head and a plurality of trial shells associated with each trialhead for use in trialing for implantation of a selected one of the oneor more bipolar hip implants.

The foregoing and other objects, features, aspects and advantages of theinvention will become more apparent from the following detaileddescription of the invention when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A-1B provide a side view cross-section of one preferred embodimentof a trial shell and trial head of the invention.

FIGS. 2A-2C provide views of one preferred embodiment of a trial shellfor use in the invention.

FIGS. 3A-3D provide views of one preferred embodiment of trial head foruse in the invention.

FIG. 4 provides a perspective view of a surgeon using orientationfeatures of one preferred embodiment of the invention in order to inserta trial head into a trial shell for using trial reduction on a patient.

FIG. 5 provides a side view of one preferred embodiment of a trialingsystem of the invention oriented on a modular femoral neck for use intrial reduction on a patient.

PREFERRED EMBODIMENTS OF THE INVENTION

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which are shown by way of illustration specific embodiments inwhich the invention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

As shown in FIGS. 1A-1B, the invention is a trialing system for use inimplanting a hip prosthesis in an acetabulum and a proximal femur of apatient. The trialing system generally comprises a trial shell 10 and anassociated trial head 40, with the components having certaincharacteristics that allow the head 40 and shell 10 to be assembled inone orientation, yet keep the head 40 locked inside the shell 10 duringtrial articulation. The invention is designed particularly for use withconstrained hip implants, and even more particularly for use withconstrained bi-polar hip implants such as the type discussed in U.S.Pat. No. 4,241,463 (Khovaylo) and U.S. Pat. No. 4,798,610 (Averill etal.), both of which are incorporated herein by reference.

As indicated in FIG. 2A, an outer surface 14 of the trial shell 10 isconfigured for receipt within an acetabulum of a patient. For bi-polarshells, the configuration of the outer surface 14 is substantiallyspherical. As shown in FIG. 2B, the trial shell 10 has a substantiallyspherical bearing cavity 12 formed therein for closely receiving thetrial head 40 during trial articulation. As indicated in the side viewcross-section of FIG. 2B, the bearing cavity 12 extends beyond 180degrees, and preferably to between about 215 and about 220 degrees, withthe range preferably selected to closely replicate the degree ofconstraint of the final acetabular shell implant. As indicated in FIG.2B, the bearing cavity 12 is accessible via a trial shell opening 20 inthe trial shell 10. The trial shell opening 20 includes a head entryportion 22 configured to allow the trial head 40 to pass through thetrial shell opening 20 and into the bearing cavity 12, as will bediscussed in further detail below. The head entry portion 22 has adiameter that is less than a diameter of the bearing cavity 12.

As indicated in FIG. 3, the trial head 40 has a bearing portion 41 and arim portion 44. The rim portion 44 is configured to receive a femoralneck during trial articulation, in a manner known to those of skill inthe art. The bearing portion 41 has a substantially spherical outerbearing surface 42, the bearing surface 42 having a diameter greaterthan the diameter of the head entry portion 22 of the trial shellopening 20. The foregoing features of the trial head 40 are known in theart. As shown in FIGS. 1 and 3, the invention improves upon the priorart trial heads by, among other things, providing a cut-out region 50formed in the outer surface 42. The cut-out region 50 is preferablycylindrical so as to closely match the head entry portion 22 of thetrial shell opening 20, although other configurations, such as a concavegroove, could be used. The cut-out region 50 has a diameter that is lessthan the diameter of trial head 40 and the head entry portion 22 of thetrial shell opening 20, a feature that enables the trial head 40 to beinserted into the trial shell 10. The cut-out region 50 is positionedsuch that when a femoral neck is disposed in the rim portion 44, thetrial head 40 is retained within the bearing cavity 12 of the trialshell 10.

As shown in FIG. 1A, when the cut-out region 50 of the trial head 40 isaligned with the head entry portion 22 of the trial shell opening 20 inan assembly orientation, the trial head 40 can pass through the trialshell opening 20 and into the bearing cavity 12 of the trial shell 10.The assembly orientation is outside the normal range of motion of thefemoral head, such that the trial head 40 will not disassociate from thetrial shell 10 during trial reduction. As shown in FIG. 1B, when thecut-out portion 50 is not aligned with the head entry portion 22, thetrial head 40 is retained in the bearing cavity 12. In particular, thespherical diameter of the trial head 40 is too large to allowdisassembly past the cylindrical portion 22 of the trial shell 10.

In the embodiment of FIG. 2B, the head entry portion 22 is cylindricaland is directly adjacent the bearing cavity 12. A preferred height ofthe head entry portion 22 is about 0.2 inches. While the height of thecylinder could have greater or lesser dimensions (including virtually noheight), 0.2 inches provides sufficient height to assist with orientingthe cut-out region 50 in the opening 20 yet without significantlycompromising the articulation characteristics of the trial system duringtrial articulation. The head entry portion 22 is preferably sized toclosely receive the cut-out region 50 of the trial head 40, which servesto optimize the size of the cut-out region 40 and maximize the surfacecontact between the spherical bearing surface 41 of the trial head 40and the bearing cavity 12 of the trial shell 10.

The cut-out region 50 could be formed at various orientations and stillenable the functionality of the invention. However, when operatingwithin the confines of a hip surgical incision, and particularly theshort incisions used in minimally invasive surgical (“MIS”) procedures,certain orientations are preferred. The inventors have concluded thatthe orientation shown in FIGS. 1 and 3 provides optimal performance. Asshown in FIG. 3A, the cut-out region 50 preferably extends along thebearing portion between opposing edges of the rim portion 44. As shownin FIG. 3C, the cut-out region 50 is preferably obliquely angledrelative to the rim 44 of the trial head 40. In a preferred embodiment,the cut-out region 50 is angled at between about 60 and about 70 degreesrelative to the rim portion 44 of the trial head 40, and is mostpreferably angled at about 65 degrees.

To assist in installing and removing the trial head 40 from the trialshell 10, an orientation indicator 60 is preferably provided on thetrial head 40. The orientation indicator 60 is positioned to indicatealignment between the cut-out region 50 of the trial head 40 with thehead entry portion 22 of the trial shell 10, such as in the orientationshown in FIG. 1A. As shown in FIGS. 3C and 3D, the orientation indicator60 is preferably a flat 60 formed along the rim portion 44. As indicatedin the side view of FIG. 3C, the flat 60 is preferably substantiallyparallel to the cut-out region 50. As further indicated in the side viewcross-section of FIG. 3D, the depicted configuration allows the surgeonto readily hold the trial head 40 by placing a thumb on the flat 60 anda finger on the underling surface of the bearing cavity 12. Further, dueto the placement and orientation of the flat 60 and cut-out region 50,the surgeon can readily insert a finger into the trial neck bore whenthe trial head 40 is in the assembly orientation in the shell 10, eitherduring insertion or removal of the head 40 from the shell 10. To furtherassist the surgeon in orientating the trial head 40, particularly duringremoval of the trial head 40 from the trial shell 10, an orientationgroove 52 can be formed along the cut-out region 50. As shown in FIG.3C, the orientation groove 52 is preferably formed between the cut-outregion 50 and the orientation indicator 60.

In operation, the trialing system of the invention is used for trialreduction of a bipolar hip implant. As indicated in FIG. 5, the proximalfemur is prepared for receipt of an appropriately sized femoral stem 70.A trial femoral stem 70 is positioned in the prepared femur. Asindicated in FIG. 5, in a preferred system, the trial femoral stem 70 isconfigured as a broach having a trial modular neck 80. The use of atrial modular neck provides advantages, such as reduced trial inventory,enhanced trial options, and facilitation of MIS procedures. However, thetrialing instruments of the invention can be used with a fixed neckfemoral stem trial. The instruments can also be used with a modular orfixed neck implant rather than a femoral trial, for example in arevision surgery.

The trialing system is used by orienting the trial shell 10 in theacetabulum of the patient, aligning the cut-out region 50 of the trialhead 40 with the head entry portion 22 of the trial shell opening 20,and inserting the trial head 40 through the trial shell opening 20 andinto the shell bearing cavity 12 in the assembly orientation, asindicated in FIG. 1A. The trial head 40 is then rotated within thebearing cavity 12 in order to bring the cut-out region 50 out ofalignment with the head entry portion 22, as indicated in FIG. 1B. Thetrial neck 80 of the femoral trial implant is then inserted into theneck bore of the trial head, in a manner known to those of skill in theart. The neck 80 can include a removable sleeve (not shown) on a trialhead receiving end of the neck for use in assessing short, medium andlong neck options, the sleeve being configured to securely associatewith the neck bore of the trial head during trial reduction. Asindicated in FIG. 4, in an alternative preferred method, the trial head40 is placed in the trial shell 10 before placing the trial head andtrial shell into the patient. The trial head-trial shell construct 10-40is then placed onto a femoral neck 80 oriented in the patient's femur.

FIG. 4 provides a perspective view of a surgeon using orientationfeatures of one preferred embodiment of the invention in order to insertor remove a trial head 40 into a trial shell 40 for use in trialreduction on a patient. Due to the orientation of the cut-out region 50,the trial head 40 cannot disassociate from the trial shell 10 while thetrial neck is in the trial head 40. This allows the surgeon to performtrial articulation without worrying about disassociation. Once trialingis complete, the surgeon removes the trial neck from the trial head 40and rotates the cut-out region 50 back into alignment with the headentry portion 22 of the trial shell opening 20, as indicated in FIG. 1A.If orientation indicators, such as the flat 60 and groove 52 of FIG. 3C,are provided, the indicators are used to insert and remove the head 40from the shell 10.

The components of the trialing system are preferably provided in theform of a surgical kit, the kit having a plurality of different sizedtrial cups and matching trial heads. The various trial sizes conform tosizes of final hip implants, which can form part of the kit. Forexample, the kit may include three sizes of trial heads 40 and aplurality of different sized shells 10 associated with each size oftrial head 10. The components of the kit are preferably arranged in aconvenient format, such as in a surgical tray or case. However, the kitcomponents do not have to be packaged or delivered together, providedthat they are assembled or collected together in the operating room foruse at the time of surgery.

As used herein, the term “substantially spherical” is intended toinclude components that are functionally spherical but which deviatefrom perfect sphericity.

Although the present invention has been described in terms of specificembodiments, it is anticipated that alterations and modificationsthereof will no doubt become apparent to those skilled in the art. It istherefore intended that the following claims be interpreted as coveringall alterations and modifications that fall within the true spirit andscope of the invention.

1. A trialing system for use in implanting a hip prosthesis in anacetabulum and a proximal femur of a patient, the trialing systemcomprising: a trial head and an associated trial shell, an outer surfaceof said trial shell configured for receipt within the acetabulum, saidtrial shell having a substantially spherical bearing cavity formedtherein for closely receiving said trial head during trial articulation,said bearing cavity extending beyond 180 degrees, said bearing cavityaccessible via a trial shell opening in said trial shell, said trialshell opening including a head entry portion configured to allow saidtrial head to pass through said trial shell opening and into saidbearing cavity, said head entry portion having a diameter that is lessthan a diameter of said bearing cavity, said trial head having a bearingportion and a rim portion, said rim portion configured to receive afemoral neck during trial articulation, said bearing portion having asubstantially spherical outer bearing surface, said bearing surfacehaving a diameter greater than said diameter of said head entry portionof said trial shell opening, a cut-out region formed in said outerbearing surface, said cut-out region having a diameter that is less thansaid diameter of said head entry portion of said trial shell opening,said cut-out region positioned such that when a femoral neck is disposedin said rim portion, said trial head is retained within said bearingcavity of said trial shell, whereby when said cut-out region of saidtrial head is aligned with said head entry portion of said trial shellopening, said trial head can pass through said trial shell opening andinto said bearing cavity of said trial shell, and whereby said trialhead is retained in said bearing cavity when said cut-out region is notaligned with said head entry portion.
 2. A trialing system of claim 1,wherein said cut-out region is cylindrical and extends along saidbearing portion between opposing edges of said rim portion.
 3. Atrialing system of claim 2, wherein said cut-out region is obliquelyangled relative to said rim of said trial head.
 4. A trialing system ofclaim 3, wherein said cut-out region is angled at between about 60 andabout 70 degrees relative to said rim portion of said trial head.
 5. Atrialing system of claim 4, wherein said cut-out region is angled atabout 65 degrees relative to said rim portion of said trial head.
 6. Atrialing system of claim 1, further comprising an orientation indicatoron said trial head, said orientation indicator positioned to indicatealignment between said cut-out region of said trial head with said headentry portion of said trial shell.
 7. A trialing system of claim 6,wherein said orientation indicator is a flat formed along said rimportion, said flat being substantially parallel to said cut-out region.8. A trialing system of claim 6, wherein an orientation groove is formedalong said cut-out region between said cut-out region and saidorientation indicator.
 9. A trialing system of claim 4, furthercomprising an orientation indicator on said trial head, said orientationindicator positioned to indicate alignment between said cut-out regionof said trial head with said head entry portion of said trial shell. 10.A trialing system of claim 9, wherein said orientation indicator is aflat formed along said rim portion, said flat being substantiallyparallel to said cut-out region.
 11. A trialing system of claim 9,wherein an orientation groove is formed along said cut-out regionbetween said cut-out region and said orientation indicator.
 12. Atrialing system of claim 1, wherein said head entry portion of saidtrial shell is cylindrical.
 13. A trialing system of claim 12, whereinsaid head entry portion is directly adjacent said bearing cavity.
 14. Atrialing system of claim 12, wherein a height of said head entry portionis about 0.2 inches.
 15. A trialing system of claim 12, wherein saidhead entry portion is sized to closely receive said cut-out region ofsaid trial head.
 16. A trialing system of claim 1, wherein said bearingcavity of said trial shell extends between about 215 and about 220degrees.
 17. A trialing system of claim 1, wherein said cut-out regionis sized to closely pass through said head entry portion of said openingof said trial shell.
 18. A method of trialing for a bi-polar hip implantin an acetabulum and a proximal femur of a patient comprising: orientinga femoral neck in the femur of the patient for use in trial reduction,providing a trial head and an associated trial shell, said trial headand said associated trial shell comprising an outer surface of saidtrial shell configured for receipt within the acetabulum, said trialshell having a substantially spherical bearing cavity formed therein forclosely receiving said trial head during trial articulation, saidbearing cavity extending beyond 180 degrees, said bearing cavityaccessible via a trial shell opening in said trial shell, said trialshell opening including a head entry portion configured to allow saidtrial head to pass through said trial shell opening and into saidbearing cavity, said head entry portion having a diameter that is lessthan a diameter of said bearing cavity, said trial head having a bearingportion and a rim portion, said rim portion configured to receive afemoral neck during trial articulation, said bearing portion having asubstantially spherical outer bearing surface, said bearing surfacehaving a diameter greater than said diameter of said head entry portionof said trial shell opening, a cut-out region formed in said outerbearing surface, said cut-out region having a diameter that is less thansaid diameter of said head entry portion of said trial shell opening,said cut-out region positioned such that when a femoral neck is disposedin said rim portion, said trial head is retained within said bearingcavity of said trial shell, whereby when said cut-out region of saidtrial head is aligned with said head entry portion of said trial shellopening, said trial head can pass through said trial shell opening andinto said bearing cavity of said trial shell, and whereby said trialhead is retained in said bearing cavity when said cut-out region is notaligned with said head entry portion, aligning said cut-out region ofsaid trial head with said head entry portion of said trial shellopening, inserting said trial head through said trial shell opening andinto said shell bearing cavity, rotating said trial head within saidbearing cavity in order to bring said cut-out region out of alignmentwith said head entry portion, securing said trial head on said femoralneck via said neck bore of said trial head, and performing trialreduction on the patient's hip using said trial head and said trialshell.
 19. The method of claim 18, further comprising, once trialing iscomplete, dissociating said trial head from said trial neck, rotatingsaid cut-out region back into alignment with said head entry portion ofsaid trial shell opening, and removing said trial head from said trialshell.
 20. The method of claim 18, wherein said trial shell is orientedin the acetabulum of the patient prior to inserting said trial head insaid trial shell.
 21. The method of claim 18, wherein said trial head isplaced in said trial shell to form a trial head-trial shell assemblybefore placing said trial head and said trial shell into the patient.22. The method of claim 18, wherein the femoral neck is modular.
 23. Themethod of claim 22, wherein the modular femoral neck is a trial modularneck.
 24. A surgical kit including a trialing system for a bipolar hipimplant for a patient comprising: one or more bipolar hip implants, eachsaid bipolar hip implant comprising a femoral stem, a bipolar acetabularshell, and a bipolar head, at least one trial head and a plurality oftrial shells associated with each said trial head for use in trialingfor implantation of a selected one of said one or more bipolar hipimplants, each said trial shell comprising an outer surface of saidtrial shell configured for receipt within the acetabulum, said trialshell having a substantially spherical bearing cavity formed therein forclosely receiving said trial head during trial articulation, saidbearing cavity extending beyond 180 degrees, said bearing cavityaccessible via a trial shell opening in said trial shell, said trialshell opening including a head entry portion configured to allow saidtrial head to pass through said trial shell opening and into saidbearing cavity, said head entry portion having a diameter that is lessthan a diameter of said bearing cavity, each said trial head comprisingsaid trial head having a bearing portion and a rim portion, said rimportion configured to receive a femoral neck during trial articulation,said bearing portion having a substantially spherical outer bearingsurface, said bearing surface having a diameter greater than saiddiameter of said head entry portion of said trial shell opening, acut-out region formed in said outer bearing surface, said cut-out regionhaving a diameter that is less than said diameter of said head entryportion of said trial shell opening of said associated trial shells,said cut-out region positioned such that when a femoral neck is disposedin said rim portion, said trial head is retained within said bearingcavity of said trial shell, whereby when said cut-out region of saidtrial head is aligned with said head entry portion of said trial shellopening, said trial head can pass through said trial shell opening andinto said bearing cavity of said trial shell, and whereby said trialhead is retained in said bearing cavity when said cut-out region is notaligned with said head entry portion.